See here for more info.
http://www.house.gov/transportation/...20-00memo.html
Essentially nothing has been proven. However, aircraft are built to exacting standards, particulalry with regard to electrical interference. This considerably increases the cost of building - all for the safety of the people on board. The mobile 'phones are not built to anywhere near the same standard, and potentially reduce safety, at no cost at all!
I believe it is also an offence to operate an airborne radio transmitter without a licence.
Finally, an airborne mobile phone can reach several transmitters (line of sight transmission). Apparently, this is not a good thing for the 'phone providers.
GB